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21 March 2012: Satellite Observations and Climate Modeling

Dr. Albert Arking, JHU, and formerly an atmospheric scientist at NASA Goddard, talked about the science behind climate change. His talk was mainly about the basic physics. Time did not allow to do more than touch the climate simulation models.

Instrument temperature measurements of land air and sea have established that the earth’s temperature has increased by about 0.8 degrees C over the past 100 years. Information prior to instrumentation depends on proxies, isotopes, tree rings, ice cores etc. Correlations between apparently independently proxies leads to confidence in the data.

A particularly impressive data set was sea level showing a 20 cm increase over the past 100 years due mainly to bulk expansion and to a lesser extent, ice melting. This was a steady increase exhibiting none of the decanal variations apparent in the temperature data. Extending this data back in time to the last ice age, 20,000 years ago showed a 130 meter rise, mainly due to ice melting.

Another data set showed four 100,000 year cycles going back 400,000 years. This cycle correlates with earth orbit changes although causal mechanisms are unclear. High/low temperature varied by 12 degrees C with no trend.

Atmospheric CO2 has increased from a base of 280 ppm to 370 ppm today due to burning fossil fuels. The last time atmospheric CO2 levels were this high was at least 15 million years ago. The question that is being asked is what happens if CO2 doubles again from here.

Solar system planet surface temperatures can be explained by a balance between incoming solar radiation and outgoing terrestrial radiation. With no feedback mechanisms it is generally accepted that doubling CO2 will increase temperature by 1.3 deg. C. The question is the amount of feedback to be expected from changing surface albedo (ice and snow), changing water vapor, and changing cloud cover. Two supposedly independent models estimate the temperature increase to be 2-4 deg. C.

The affect of aerosols seem to wash. Most aerosols have and overall cooling effect though highly absorbing aerosols can contribute to warming. Aerosols flush out of the atmosphere within a few years.

There is a fascinating correlation between northern hemisphere land air temperature and the length of the solar sunspot cycle going back 500 years. Causal relationships are unclear. This solar relationship seems to explain 1/3 of the observed temperature rise over the past 50 years.

Dr Arking concluded with 2007 Intergovernmental Panel on Climate Change (IPCC) scenarios where 2100 global temperatures ranged between 1.4 and 4 deg. C. He had no comment on tipping points such as global warming shutting down the Gulf Stream or releasing methane from permafrost. Dr Arking concluded that the country needs a similar effort like the way NASA took on the race to the moon. Develop and deploy a new technology that can slow down the temperature increases over the next century.